JPS6247003B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention reduces the influence of ambient noise by controlling the amplification degree of an audio amplifier according to the input level of an audio signal input via a transmitter (microphone), etc. The present invention relates to a transmitting device.

Generally, an audio amplifier that amplifies an audio signal outputs an audio signal proportional to its input level.

By the way, when amplifying the audio signal output from a transmitter, the voice of the speaker is input to the transmitter as a relatively strong sound pressure during transmission, so surrounding noise is masked by the voice. , I don't mind if it's a little noisy. However, when the transmission is interrupted, there is only ambient noise, which is amplified and output as it is, so it is noisier than when the voice is transmitted.

Conventionally, a method to reduce this problem was to operate the audio amplifier at low gain until the audio level input reaches a certain level Pa, and at higher gain at higher levels. When audio is input, the amplified output level fluctuates rapidly, impairing the naturalness of the transmission.
Furthermore, if the gain difference is made smaller in order to prevent this, there is a drawback that the degree of improvement with respect to ambient noise becomes smaller.

This invention was made in order to eliminate the drawbacks of the conventional devices, and when the input to the transmitter is low or when there is only ambient noise, the input and output characteristics of the transmitter are given an expansion characteristic, and the transmitter is When the transmitter input is high, by providing a general direct proportionality characteristic, it is possible to prevent the output from changing stepwise due to the magnitude of the transmitter input level, reduce the influence of ambient noise, and not leave any unnaturalness in the transmission. The present invention provides a transmitting device.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a transmitter into which an audio signal is input, and the output of the transmitter 1 is applied to the input of an audio amplifier 2 and an audio signal expander 4, respectively. Audio input from a transmitter 1 is amplified to an optimal level by an audio amplifier 2 and rectified by a rectifier circuit 3. A ripple component of the rectified output of the rectifier circuit 3 is removed by a smoothing circuit 8 composed of resistors R ₁ and R ₂ and a capacitor C ₁ . The output of this smoothing circuit 8 is then applied to one input terminal of the voltage comparator 6. On the other hand, the audio signal expander 4
When the sound pressure level to transmitter 1 reaches the _P1 level, if the input level changes by 1 dB, the output will be
The output of the audio signal expander 4 is rectified by the rectifier circuit 5. This rectified output is connected to resistors R ₃ , R ₄ and capacitor C ₂
The ripple is removed by a smoothing circuit 9 and applied to the other input terminal of the voltage comparator 6. Further, the output of the audio amplifier 2 and the output of the audio signal expander 4 are each connected to a different molecule input terminal of an analog switch 7, and the configuration is such that one of them is selected and outputted by a control signal from the voltage comparator 6. has been done.

Voltage comparator 6 compares the smoothed output voltages respectively output from smoothing circuits 8 and 9, and outputs it as a control signal for analog switch 7 so as to select one of them with a lower level.

FIG. 2 shows the input/output characteristics of the transmitter shown in FIG.

Next, the operation shown in FIG. 1 will be explained using FIG. 2.

In Figure 2, the characteristics of (A) are the sound pressure input Pi of the transmitter 1,
This is the characteristic of the output V ₀ of the audio signal expander 4. In other words, from a sound pressure input below P ₀ to Pi, there is a proportional change of 1 dB for a 1 dB change in input, but for a 1 dB change in input when the sound pressure input exceeds P ₁ , the output changes.
It has a characteristic that causes a change of 2dB.

On the other hand, the characteristics in (B) are the characteristics of the sound pressure input Pi of the transmitter 1 and the output V ₀ of the audio amplifier 2, and the audio output V ₀ is obtained which is directly proportional to the audio input Pi.

Now, when the input sound pressure Pi to the transmitter 1 is lower than Pa, the output of the audio signal expander 4 is lower than the output of the audio amplifier 2, as shown in FIG. Therefore, the voltage comparator 6 outputs a control signal that causes the analog switch 7 to select the audio signal expander 4.

Next, the input Pi to the handset gradually increases and Pa
When the level reaches or above, the smoothed output of the input of the voltage comparator 6 on the audio amplifier 2 side becomes low, so the voltage comparator 6 selects the audio amplifier 2 side, and the analog switch 7 switches and outputs the amplified output. In other words, it will undergo the characteristic (B).

In a normal transmitting state, the input sound pressure is in a region greater than Pa, and the input sound pressure of the transmitter and the output of the transmitter are directly proportional. If the input to the transmitter is only ambient noise and the sound pressure is less than P ₁ , the output will be lower by (Vb - V ₀ ) dB compared to a conventional transmitter in which the input and output are proportional, so the ambient noise will be reduced. The degree of harshness will decrease. When the sound pressure is between _P1 and Pa, the gain changes at a ratio of 1:2 depending on the amount of sound pressure input.

In this way, compared to conventional speech transmitting devices, the change in output due to large changes in sound pressure input is not stepwise, so that natural output can be obtained even in response to the intonation of speech during speech transmission.

Note that the step response of the smoothing circuit when the transmitter input is suddenly changed, that is, the speed of switching between the audio amplifier 2 and the audio signal expander 4 is R ₁ , R ₂ , C ₁
and determined by the values of R ₃ , R ₄ , and C ₂ . Therefore, in order to prevent the beginning of a word from being cut off at the beginning of the voice,
R ₁ C ₁ = t ₁ or R ₃ C ₂ = R ₂ C ₁ = t 3 or R ₃ C ₂ in order to shorten t ₂ and keep the change in tone _constant during transmission.
= R ₁ < R ₂ is selected so that t ₄ is made long.

By the way, when the input sound pressure is close to Pa, a so-called chattering phenomenon occurs in which the outputs of the audio amplifier 2 and the audio signal expander 4 appear as outputs of the transmitting device. This is because a slight change in the input of the voltage comparator 6 causes its output to change. In order to prevent this, the voltage comparator 6 may be provided with hysteresis characteristics.

As described above, according to the present invention, the audio signal expander is used in a range where the sound pressure input to the transmitter is low, such as ambient noise, and the audio signal expander is used in a range where the sound pressure input to the transmitter is high, such as in normal voice transmission. Since the signal passed through an audio amplifier with a proportional output is output as a transmitter, the noisiness when only ambient noise is input to the transmitter is improved, and the degree of improvement is based on changes in sound pressure. Since the output characteristic changes smoothly according to the speech rate, it is possible to obtain a natural transmitting device output characteristic even in response to the intonation of speech during a conversation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a transmitter according to an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing the input/output characteristics of FIG. 1 is a transmitter, 2 is an audio amplifier, 3 and 5 are rectifier circuits, 4 is an audio signal expander, 6 is a voltage comparator, 7 is an analog switch, and 8 and 9 are smoothing circuits. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A first amplifier that amplifies an input audio signal with a constant gain, when the audio signal level is below a predetermined level, the gain is lower than that of the first amplifier, and when the audio signal level is above a predetermined level, the gain is lower than that of the first amplifier. a second amplifier that amplifies the audio signal with a higher gain than the amplifier; a first amplifier that rectifies and smoothes the amplified outputs of both amplifiers;
and a second rectifier/smoothing circuit, a voltage comparator that compares the output levels of these two smoothing circuits and outputs a control signal corresponding to the smaller level side, which is switched and controlled by the control signal of this voltage comparator, and 1. A transmitter comprising a switch circuit for switching and outputting the amplified output of the first or second amplifier. 2 Rise of the first and second smoothing circuits (charging)
2. The transmitting device according to claim 1, wherein the transmitting time is configured to be shorter than the falling (discharging) time. 3. Claim 1 or 2, characterized in that the voltage comparator outputs a two-state signal depending on the magnitude of the output level of the first and second smoothing circuits.
Transceiver device described in section. 4. The transmitting device according to claim 3, wherein the voltage comparator has a hysteresis characteristic.